Keywhiz is a secret management solution built by Square. Keywhiz has a
client/server architecture based on a RESTful API. Clients of Keywhiz access
secrets through the API by authenticating with a client certificate or cookie.
To allow for flexible consumption of secrets by arbitrary software, clients may
also make use of a FUSE filesystem to expose secrets as files on disk, and use
Unix file permissions for access control. Human operators may authenticate
using a cookie-based authentication either via command line utilities or
through a management web interface.

Vault similarly is designed as a comprehensive secret management solution. The
client interaction with Vault is flexible both for authentication and usage of
secrets. Vault supports mTLS authentication along with
many other mechanisms. The goal is to make it easy
to authenticate as a machine for programmatic access and as a human for
operator usage.

Vault and Keywhiz expose secrets via an API. The Vault ACL
system is used to protect secrets and gate
access, similarly to the Keywhiz ACL system. With Vault, all auditing is done
server side using audit devices.

Keywhiz focuses on storage and distribution of secrets and supports rotation
through secret versioning, which is possible in the Keywhiz UI and command-line
utilities. Vault also supports dynamic secrets and generating credentials
on-demand for fine-grained security controls, but adds first class support for
non-repudiation. Key rotation is a first class concern for Keywhiz and Vault,
so that no external systems need to be used.